How to Find Drafts in Your House: Where Air Leaks Hide and How to Check

To find drafts, check the places air usually leaks, then test each one. ENERGY STAR says to feel for cool air with a damp hand, close a sheet of paper in each window and door, and look for light shining through gaps. For hidden leaks, it suggests turning on your exhaust fans with the windows shut and watching where incense smoke wavers. Start with the attic hatch, recessed lights, the pipe and wire holes, outlets, windows and doors, baseboards, the fireplace damper, and the rim joist in the basement. ENERGY STAR says the biggest leaks in most homes are hidden in the attic and basement, not at the windows.

If one room is cold and the rest of the house is fine, start with one room colder than the rest.

Why Drafts Show Up in Winter

ENERGY STAR says warm air rises through the house like smoke up a chimney, escapes into the attic, and pulls cold air in around windows, doors, and basement holes. So the draft at a window may be driven by a leak upstairs, often hidden under insulation.

Where Drafts Usually Are

Check them in this order. The list draws on ENERGY STAR's guide to common household air leaks and the U.S. Department of Energy's Energy Saver Guide.

1. The attic hatch or attic stairs. Both ENERGY STAR and DOE list the attic entrance as a leak point.
2. Recessed “can” lights. ENERGY STAR says recessed lights in a top-floor ceiling leave open holes into the attic. In winter they draw warm air up, and in cold climates that heat can help form ice dams.
3. Plumbing, wiring, and duct holes. DOE says to seal leaks wherever plumbing, ducts, or electrical wiring pass through walls, floors, ceilings, and the soffits over cabinets. ENERGY STAR adds the plumbing vent, flue and duct chases, and dropped soffits over cabinets and vanities, which can hide open cavities into the attic.
4. Outlets and switches. DOE lists outlets and switch plates as leak points and suggests foam gaskets behind the cover plates.
5. Windows and doors. DOE says to look for gaps, worn caulk and weatherstripping, and windows and doors that don't close tightly. ENERGY STAR's leak map includes both door frames and window frames.
6. Baseboards and trim. DOE names gaps around window trim and baseboards as places to seal.
7. The fireplace damper. DOE says to check that the damper closes properly.
8. The basement rim joist. ENERGY STAR says a common basement leak runs along the top of the foundation wall, where the house framing sits on it. That framing is the rim, or band, joist. Air can come in through cracks and gaps there because that part of the wall is above ground.

How to Check for Drafts Yourself

Start by looking, then use ENERGY STAR's four simple tests: a damp hand, paper, a flashlight, and smoke. Do the first three before you try smoke.

1. Look first. Walk the house and note every crack and gap you see, so you can come back and seal them later (ENERGY STAR). In the attic, dirty insulation shows where air moves through (ENERGY STAR).
2. Feel with a damp hand. Wet your hand and move it slowly around a window, door, or outlet. ENERGY STAR says leaks will feel cool.
3. Try the paper test. Close a window or door on a sheet of paper. ENERGY STAR says that if you can pull it out without tearing it, you have a leak.
4. Use a flashlight at night. ENERGY STAR's light test: one person shines a flashlight over the gaps while a partner watches from outside, and light coming through means a leak. With the lights on inside, you can also look for light from the attic, crawl space, or basement, and around window and door edges.
5. Depressurize the house for the smoke test. ENERGY STAR's steps: pick a cool, very windy day and first turn off combustion appliances such as gas furnaces and water heaters. Shut all windows, exterior doors, and fireplace flues. Turn on every exhaust fan that blows outside, such as bath fans and the range hood. Then hold a lit incense stick, or dust some talcum powder into the air, around the edges of the usual leak spots. Wherever the smoke wavers or gets pulled in or out, there's a leak. DOE describes the same test with incense or a smoke pen.
6. Turn everything back on. When you finish, put out the incense, turn off the fans, and switch the furnace and water heater back on.

Talcum powder does the same job without a flame, so use it where you can. If you use incense, keep it well away from curtains and blinds and never set it down lit.

What You Can Fix Yourself

• Weatherstrip doors and windows. DOE lists it first, and ENERGY STAR says thicker weatherstripping can tighten a loose window. Our weatherstripping guide compares the types.
• Caulk small gaps. ENERGY STAR recommends caulk for gaps of 1/4 inch or less and spray foam for gaps from 1/4 inch to about 3 inches. For a larger gap behind window or door trim, it suggests non-expanding foam or backer rod.
• Add outlet and switch gaskets. DOE suggests foam gaskets behind the cover plates.
• Seal the attic hatch. ENERGY STAR's guide finishes attic sealing by weatherstripping the hatch with self-sticking foam, adding wood stops if the hatch sits right on the trim, and gluing rigid foam insulation to the back. DOE suggests an insulated box for leaky attic stairs.
• Seal the rim joist. ENERGY STAR says to seal the top and bottom of each rim joist cavity in an unfinished basement, plus the wire and pipe holes in the basement ceiling.
• Close the damper. Check that it shuts properly (DOE).
• Cover drafty windows for the winter. ENERGY STAR has a project for putting plastic film over windows, and DOE suggests tight-fitting insulating shades for windows that still feel drafty after you've sealed them. See window insulation kits.

What Not to Do

• Don't seal around flues with foam or insulation. ENERGY STAR says furnace and water heater flues can get very hot. It notes that codes usually require 1 inch of clearance from metal flues and 2 inches from masonry chimneys to anything combustible, insulation included. It seals that gap with metal flashing and high-temperature caulk, not spray foam.
• Don't block combustion air or vents. ENERGY STAR warns that sealing can, in some cases, make naturally venting appliances back-draft exhaust into the house. Leave every vent, flue, and air supply for a furnace, water heater, boiler, or fireplace open.
• Don't pack insulation around old recessed lights yourself. ENERGY STAR says sealing them is difficult and can create a hazard if it isn't done with noncombustible materials. Older fixtures need air space to vent their heat, so it says to talk to a professional first.
• Don't work over knob-and-tube wiring. ENERGY STAR calls it a fire hazard when it touches insulation.
• Take care with old painted trim. In homes built before 1978, ENERGY STAR warns that work on window and door trim can create dangerous lead dust, and it suggests hiring a professional if the home has lead paint.

When to Call a Pro

ENERGY STAR says to consider a home energy professional for a full energy audit to find hidden leaks, pinpoint fixes, and spot safety issues. DOE says a detailed assessment can include a house air leakage test, a duct leakage test, or an infrared scan, along with safety tests. Call when:

• You have gas or oil appliances and plan to tighten the house. ENERGY STAR suggests having a contractor test that those appliances draft properly before and after sealing. Its DIY guide says a tighter house can let carbon monoxide build up if gas appliances aren't venting right, so have your heating technician check the furnace, water heater, and dryer.
• Bath, kitchen, or dryer vents end in the attic instead of outdoors (ENERGY STAR). See bathroom fan vents into the attic.
• You find wet insulation, moldy or rotted framing, little or no attic ventilation, or a history of ice dams. ENERGY STAR lists all of these as reasons to bring in a contractor before you seal.
• You have lots of unsealed recessed lights (ENERGY STAR).
• The leak is in the ductwork. DOE says duct repairs should go to a qualified professional and that all duct sealing should be tested for combustion safety and proper airflow.

ENERGY STAR also says sealing can trap indoor pollutants such as carbon monoxide and radon, and that some homes may need added mechanical ventilation. Make sure you have working CO alarms; NFPA says to put them outside each sleeping area and on every level. See missing CO alarms.

Prevent It

• Check every fall. Walk the house before it gets cold and look for the gaps, worn caulk and weatherstripping, and loose-closing windows and doors that DOE says to check for. Our winter prep planner puts it on the list.
• Seal from the top down. ENERGY STAR says the biggest leaks are usually in the attic and basement, so seal those before you buy more window film.

Frequently Asked Questions

What is the easiest way to find a draft?

Move a damp hand slowly around windows, doors, and outlets; ENERGY STAR says leaks feel cool. For windows and doors, add the paper test: if you can pull a sheet of paper out of a closed sash or door without tearing it, it leaks.

Can I use a candle to find drafts?

Skip the candle. ENERGY STAR and DOE use incense or a smoke pen, and ENERGY STAR also suggests talcum powder, which has no flame at all. If you do use incense, keep it away from curtains and anything else that can burn, and never leave it unattended.

Is it safe to run all the exhaust fans to find leaks?

Only after you turn off gas and oil appliances such as the furnace and water heater, which is ENERGY STAR's first step. Turn them back on when you're done.

The Bottom Line

Look, feel with a damp hand, try the paper and flashlight tests, and save smoke for last, with the fans on and gas appliances off. Seal what you find, attic and basement first. Leave flues, combustion air, and old recessed lights alone, and with gas appliances, have venting checked or get an energy audit.

Sources

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